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Old 16th April 2007, 04:28 AM   #1
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Default Spring Reverb transformer

I have an accutronics 'verb tank that I'd like to put to good use. Its got a 600 ohm input and 2.5k output. Its model number is 4EB2c1b. There is a table on accutronics website that lists what all this means, and it was generally used in peavey amps, but has found its way into modern hotrod deluxes as well as a few other fender amps.

Its obviously for use with a solid state driver, but I'd like to use a tube driver/recovery section.

I have a few options: 1: standard 8 ohm output transformer, into a radio shack 8 ohm to 500 ohm isolation transformer, or 2: some other sort of transformer to meet the right impedance.

I was wondering, if I found a 120v:4.5v transformer ( I have one) , wouldn't this give me the appropriate impedance ratio? If I had the 600 ohm tank on the 4.5v section, wouldnt that give me around 25,000 ohms in the primary (120v winding) allowing me to use a 12at7 to drive it?

Any thoughts? Any other opinions on how to couple this would also be greatly appreciated. One that I thought of was using a small power pentode or triode with a 2.5k nominal load resistance to direct drive a 2.5k 'verb tank, as they sell tanks with a 2.5k in and 2.5k out.

As a last note, direct coupled would make for a better sound now wouldnt it?

~TSD88
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Old 16th April 2007, 11:05 PM   #2
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600 ohm line output transformers are not uncommon. Lundahl makes the LL1660, but at $80 it might be more than you want to spend. Keep your eye on eBay, or just buy a replacement unit for a hotrod Deluxe?

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Old 17th April 2007, 12:00 AM   #3
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You don't need a lot of bandwidth for a reverb tranny, so just grab the cheapest one you can find. I have used Hammond 125 series before, as well as a wall wart like you suggested.

I have also cap-coupled reverb drivers as well... it is not out of the quesstion with a 600 ohm tank... in fact, it would be rather easy. If you don't want to do the math... just look up a tube OTL headphone amp schematic for driving high impedance headphones like the 600 ohm AKG's and you should be able to drop the circuit in with very little modification.

My particular cap coupled driver was an ECL86 that used the pentode as the driver and the triode as the recovery... worked pretty well, not SUPER wet sounding, but it did the job. I think the tank had a 2.5k input though
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Old 17th April 2007, 04:39 PM   #4
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Look at Traynor amps from the late 60s and early 70s. Most of them used a 6bq5 through a cap to drive a higher impedance pan. I have several Traynor's with this reverb circuit. It's not as deep as the Fender reverb amps but close.... Google Traynor YRM-1.....
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Old 17th April 2007, 05:19 PM   #5
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For a small reverb spring, you don't want too much bass drive I've rebuilt a Fisher spacexpander, with a 12AU7 cathode follower as a 600? driver (nasty) and I rolled all the low frequencies off. A nice, cheap transformer works as a highpass all on its own.
How much voltage drive does it need? Because a mini power amp planned to drive into 15?, with a parallel resistor so the tubes see the impedance they're expecting- Still, I expect the little power transformer would have a perfectly acceptable frequency response, for that purpose.
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Old 18th April 2007, 01:33 AM   #6
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hmm ok, well I tried to post the other day but IE screwed up and locked up my pc... so it deleted my post, and I dont feel like redoing it all. blah!


I was going to ask how well your power supply output transformer worked?

I hadn't thought of an OTL headphone amp, but that makes perfect sence. Thanks for the info on the traynor, I will look that up.

And as far as bandwidth your right. Since reverb is just an echo of the mid frequencies, you dont need high and low responce, and since its mixed with the signal anyways that pretty much takes care of it. I would like to copy a fender reverb unit sometime, but for now I dont have the mula and have some tubes laying around , a few trannies, and the aformentioned verb tank. Just wanna throw together something cheap that works good. I am hoping to improve on and come up with my own design to put into my line of amplifiers.

Hmm... while I'm at it, an EL84 sounds like a waste of tube to me to just put in a 'verb unit, but its cheap and I guess makes sence. I wonder though.. maybe the sonics would be improved over a 6v6/6k6 or whatever. Could have an interesting tone. Thats the great thing about the guitar world, as some tubes that sound silly in one application may make magic for one player. Still would be nice to use a smaller tube like a 12at7 or 12au7/bh7 etc.
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Old 18th April 2007, 04:17 AM   #7
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The reverb driver just jiggles the springs... so I would not obsess over the tone too much, leave that for the recovery stage.

You'll have to get about a watt or so of drive to the tank, which has a relatively low impedance, so a transformer is the most efficient way. If you want to use a tranny... you could easily drive a tank with a little noval 9-pin triode. You can do it without a trannt too, but you won't get much spring-jiggling going on. I have tried it just for kicks, and it works... but is not very wet.

You can also easily drive a 600-2k ohm tank with a power tube if you want to avoid a tranny. I don't know if I would consider an EL84 a waste in this situation since they are cheap anyway and you are also saving the price of a tranny.
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